Compositions having isocyanate functional components are utilized in a variety of useful products such as adhesives, sealers, molded products and foams, which may be utilized in construction, vehicle manufacture, assembly of electronic subassemblies and devices, and toys. The adhesives have found widespread use because they provide reasonable processing conditions and exhibit good adhesion to many substrates, such as bonding windows into structures, or parts to a structure. In automotive assembly plants windows are bonded in with one part adhesive compositions containing isocyanate functional components and a cure catalyst which cure as a result of exposure to moisture. The dispensing equipment for one part adhesives is less complex than the equipment used to apply two-part adhesives. One part moisture curing adhesives known in the art are disclosed in U.S. Pat. No. 4,374,237, U.S. Pat. No. 4,687,533, U.S. Pat. No. 4,780,520, U.S. Pat. No. 5,063,269, U.S. Pat. No. 5,623,044, U.S. Pat. No. 5,603,798, U.S. Pat. No. 5,852,137, U.S. Pat. No. 5,922,809, U.S. Pat. No. 5,976,305, U.S. Pat. No. 5,852,137 and U.S. Pat. No. 6,512,033, relevant portions incorporated herein by reference and examples include BETASEAL™ 15630, 15625, 61355 adhesives available from The Dow Chemical Company, EFBOND™ windshield adhesives available from Eftec, WS 151™, WS212™ adhesives available from Yokohama Rubber Company, and SIKAFLEX™ adhesives available from Sika.
Two-part polyisocyanate based adhesives comprise, in one part, a polyisocyanate or an isocyanate functional prepolymer and, in a second part, a curing agent and catalyst for the reaction. The two parts are contacted to start cure and cure much faster than one-part adhesives. Examples of such adhesive systems are disclosed in U.S. Pat. No. 7,892,395; U.S. Pat. No. 6,965,008; EP 1433802 and EP 1578834, all incorporated herein by reference. Two part adhesives can be used for bonding replacement windows into vehicles, bonding parts together or parts to structures.
In automobile factories windows are installed using robots and computer controlled processing which facilitates the use of a variety of high performance adhesives, for instance nonconductive adhesives and high modulus adhesives. The speed of cure is not a significant issue because new vehicles are not driven a significant distance for several days after window installation. Conversely, when a vehicle needs a window replaced, it is often performed in a remote location by an installer working from a vehicle. In this environment, speed of cure is important as the vehicle owner desires to drive the vehicle as soon as possible after installation of the window. Adhesives useful in replacing windows for vehicles which facilitate fast drive away times are known see Bhat, U.S. Pat. No. 5,976,305 and Zhou, U.S. Pat. No. 6,709,539. The introduction of various high performance adhesive compositions used for installing windows in automobile factories presents a problem for replacement window installers. Adhesives that meet all the varied performance requirements are not available in the market place. It is difficult to formulate many high performance adhesive compositions to allow rapid drive away times that do not sag or string. Sag is the loss of the shape of the adhesive bead, often as the result of gravitational forces. If severe enough, this deformation can interfere in the proper installation and sealing of the window into the vehicle. Stringing of an adhesive is the formation of a long string of adhesive at the end of the bead of adhesive dispensed which can complicate application of the adhesive and cause imperfections in the installed adhesive bead. A replacement window installer often has to carry a variety of adhesives to match the replacement adhesive to the properties of the original adhesive.
Adhesives have been developed which provide good initial green strength that allow adhesives to hold the glass in place without fixturing. This is achieved through the inclusion of crystalline polyesters in the adhesive which have hot melt properties requiring that the adhesive be melted and applied hot; Proebster, U.S. Pat. No. 5,747,581, incorporated herein by reference. The problem with these adhesives is that they require heat and complex equipment for their use. The initial green strength may not be sufficient for rapid drive away time. Because of the proliferation of hot melt adhesives in automobile window replacement, many installers insist on heating adhesives prior to applying the adhesive to the window or the window flange, which may exacerbate sagging and/or stringing.
Several approaches to providing non-conductive adhesives including using non-conductive carbon black and polyester polyols in adhesive formulations are known U.S. Pat. No. 7,101,950. WO 02/053671 discloses the use of low or non-oxidized carbon black with polycarbonate based polyols to achieve this objective. The problem is that low conductive carbon black and polycarbonate polyols are significantly more expensive than standard grades of carbon black which are conductive and other polyols. Zhou US2006/0096694A1 discloses an adhesive which achieves a variety of high performance properties which contains polyester polyols and standard carbon black. The nonconductive properties are imparted by carefully limiting the amount of carbon black. The amount of carbon black impacts the rheological properties of the adhesive and thus the sag and stringiness of the adhesive. Polyester based isocyanate functional prepolymers are used to improve fixturing properties. As automotive designs have changed more robust adhesive systems are required. Polyester based isocyanate functional prepolymers can be shear sensitive and processing of adhesives containing them can negatively impact the properties of the adhesive and some of these adhesive systems may not be suitable for use with the new designs.
What is needed is compositions which are useful as adhesives for bonding glass into structures which may be formulated to exhibit a variety of high performance properties (such as high modulus and nonconductive nature), exhibit fast safe drive away times when applied under a variety of conditions, fast strength development, can be applied without heating the adhesive, can be applied under a wide range of environmental conditions, do not require expensive ingredients, do not sag or string when applied and exhibit improved shear sensitivity.